Energetic Electron Pitch-angle Distributions in the Martian Space Environment: Pancake

Abstract

Abstract We perform a statistical investigation of the occurrence rates of energetic electron (100–500 eV) pancake pitch-angle distributions (PADs) in the Martian space environment by utilizing 6 yr of MAVEN data. In the Martian ionosphere, we find the following: (1) at the same altitude in the terminator and night regions, the occurrences rates in the center of the southern magnetic anomaly regions are very low, but at the edges of strong magnetic fields, they increase significantly; (2) the occurrence rates of energetic electron perpendicular anisotropies on the Martian dayside increase with altitude; and (3) some closed magnetic lines in the 10°S–55°S, 30°W–125°W region at 400–800 km altitude gradually become open during the rotation of Mars from duskside to dawnside, while more closed magnetic lines are produced in the 40°S–65°S, 35°E–90°E region. In the Martian induced magnetosphere, we find the following: (1) the high-energy electron perpendicular anisotropy in the magnetosheath is the most significant; (2) the occurrence rates in the southern (Z MSO ≤−1 R M) magnetosheath are higher than those in the northern (Z MSO ≥ 1 R M) magnetosheath; (3) in the region of ∣Z MSO∣ < 0.5 R M, these high-energy electron pancake PADs are mainly concentrated in the magnetosheath region with Y MSO ∈ [−1.4RM, 2R M]; (4) the occurrence rates in the dawnside (Y MSO ≤−1 R M) magnetosheath are higher than those in the duskside (Y MSO ≥ 1 R M) magnetosheath; and (5) in the region of ∣Y MSO∣ < 0.5 R M, the occurrence rates throughout the magnetosheath are very high.